A catalyst containing a titanium compound supported on a halogenated magnesium in an active state has been known conventionally as a catalyst used for producing olefin polymers such as ethylene, an α-olefin homopolymer, and an ethylene.α-olefin copolymer, etc. (Hereinafter, the meaning of polymerization occasionally includes not only homopolymerization but also copolymerization such as random copolymerization, block copolymerization, etc.)
As such an olefin polymerization catalyst, widely known are a catalyst called as Zeigler-Natta catalyst which comprises titanium tetrachloride or titanium trichloride and a catalyst which comprises an organometallic compound and a solid titanium catalyst component comprising magnesium, titanium, halogen and an electron donor.
The latter catalyst shows high activity for polymerization of ethylene, and α-olefins such as propylene, butene-1, etc. Moreover, a resulting α-olefin polymer sometimes has high stereoregularity.
JP-A-S58 (1983)-83006 (Patent Document 1) and JP-A-S56 (1981)-811 (Patent Document 2) disclose when, of these catalysts, a solid titanium catalyst component on which an electron donor selected from carboxylic acid esters typified by phthalic acid ester is supported, an aluminum-alkyl compound as a co-catalyst component and a silicon compound having at least one structure represented by Si—OR (in the formula, R is a hydrocarbon group) are used particularly, excellent polymerization activity and stereospecificity can be realized.
It is known that the enlargement of a catalyst particle diameter is preferred from the viewpoints of “increasing of the rubber amount in the preparation of impact copolymers” or “prevention of particles from scattering in a gas phase step”. The methods as described in the above patent documents include a step of allowing a magnesium compound in a liquid state to contact with a titanium compound in a liquid state. The documents further disclose that the resulting polymers prepared using these catalysts show good morphology and can be prepared by a relatively simple method, but it is difficult to enlarge the catalyst particle diameter.
As a method for producing a catalyst having a large particle diameter, there are disclosed a method of using an adduct having a large diameter comprising MgCl2 and ethanol as a carrier (JP-A-2004-2742 (Patent document 3) etc), a method of using a carrier having a large particle diameter such as Mg(OEt)2, SiO2, etc (JP-A-2001-114811 (patent document 4) etc) and a method of preparing a polymer having a large particle diameter by using various alcohols and cyclic ethers and thereby controlling the sizes of catalyst particles in the preparation of a magnesium compound having no reducing ability in a liquid state (JP-A-H10 (1998)-316712 (Patent document 5) etc). These methods, however, have tendencies that the production process is complicated and the production cost is high.
Meanwhile, there is a trend such that the use of polyfunctional aromatic compounds such as phthalic acid esters etc is restrained from the safety and hygienic problems. Against the trend, almost of reports including the above patent documents disclose examples that polyfunctional aromatic compounds such as phthalic acid esters are used preferably as an electron donor. Patent document 4 discloses that a catalyst free from aromatic esters is prepared by using the simple production process disclosed in Patent document 1 or Patent document 2. However, it is not said that the resulting catalyst is free of polyfunctional aromatic compounds because of using a phthalic anhydride as a starting material.
Patent document 1: JP-A-S58 (1983)-83006
Patent document 2: JP-A-S56 (1981)-811
Patent document 3: JP-A-2004-2742
Patent document 4: JP-A-2001-114811
Patent document 5: JP-A-H10 (1998)-316712